It is an article of faith among many mainstream experts that poor posture, lack of core strength, and/or structural abnormalities such as bulging discs are major causes of pain, especially back pain. A further assumption is that by working to correct such imbalances, through stretching or strengthening regimes, or surgery, the imbalances can be corrected and pain will decrease. It is probably fair to say that the majority of physical therapy and corrective exercise that is done in this country is based on exactly these assumptions. Although these ideas have a common sense appeal, there is significant evidence questioning this approach. Here’s a brief review of the conflicting evidence.*
The idea that bad posture causes pain, especially back pain, is ubiquitous. A google search for posture and pain shows 4 million hits and reveals many sites devoted exclusively to improving posture. With so many posture police on patrol, you will almost certainly be advised sooner or later that your posture is causing you pain or will cause pain in the future if you don’t fix it. If you go to a physical therapist with low back pain and a big curve in your low back, you will almost certainly be told that you need to suck in your gut, squeeze your glutes, tuck your tail, tighten your abs, and strengthen your core. If you have upper back pain and a sunken chest, you will be told to pinch back your shoulder blades, strengthen your scapular retractors, stretch the chest, and raise the sternum, until you look like a rooster. Before running off to do these exercises, let’s see what the studies have to say about the link between pain and posture.
In one study, researchers looked at the posture of teenagers and then tracked who developed back pain in adulthood. Teenagers with postural asymmetry, thoracic kyphosis (chest slumping) and lumbar lordosis (overly arched low lack) were no more likely to develop back pain than others with “better” posture.
Another study looked at increases in low back curve and pelvic angle due to pregnancy. The women with more postural distortion were no more likely to have back pain during the pregnancy. Another study found that adults with lumbar scoliosis and increased low back curve were no more likely to have back pain than others. Other studies have shown no association between pelvic asymmetry, sacral base angle and low back pain. Leg length inequality seems to have no effect on back pain unless it is more than 20 mm (the average leg length difference is 5.2 mm). Hamstring and psoas tightness do not predict back pain, and there is strong evidence that orthotics do not prevent back pain.
These results are particularly striking given that many studies have quite easily found other factors that correlate well with low back pain, such as exercise, job satisfaction, educational level, stress, and smoking. Although some studies have found a correlation between back pain and posture, it is important to remember the rule that correlation does not equal causation. It may be that the pain is causing the bad posture and not the other way around. This is a very likely possibility. Studies show that patients will spontaneously adopt a different posture when injected with a painful solution (big surprise!). I think these researchers should have won a major prize.
Based on the above, there is little evidence to support the idea that we can explain pain in reference to posture or that we can cure pain by trying to change posture.
Disc Degeneration and Other MRI Abnormalities
Another common idea is that herniated discs or other degenerative changes revealed by an MRI are major causes of back pain. If you have back pain and get an MRI or x-ray that shows degenerative changes near the area of pain, such as a bulging or herniated disc, the doctor will likely conclude that the pain is due to what is seen on the MRI. The doc may even recommend surgery to correct the structural defects. However, numerous studies show that many types of structural abnormalities are poor predictors of pain.
In one famous study, MRIs were performed on subjects who did not have back pain. Fifty two percent of the subjects had at least one bulging disc or other MRI abnormality for which surgery is often recommended. In a study of pain free hockey players, seventy percent were found to have abnormal pelvis or hip MRIs, and fifty four percent had labral tears. Studies of active baseball pitchers or overhead athletes consistently demonstrate very large percentages (over seventy percent) of torn labrums and rotator cuffs. Another study showed forty percent of pain free overhead athletes had partial or full thickness rotator cuff tears. One third of asymptomatic people over the age of forty have rotator cuff tears. These people have full pain free shoulder function. MRIs on asymptomatic knees show that thirty four percent have tears of the meniscus. Forty seven percent of professional pain free basketball players show articular cartilage lesions in their knees. These are all issues for which surgery is sometimes recommended.
This is not to say that herniated discs, torn labrums or other structural abnormalities cannot cause pain. Of course they can, and you would rather have less damage than more. But if a large percentage of pain free people have bulging discs, then how likely is it that a bulging disc is the cause of your back pain? If you look close enough at almost any joint in the body, you will find something wrong with it. Don’t assume that whatever shows up on the MRI is the source of your pain.
The idea that good core strength is essential for a healthy back is another ubiquitous idea. If you go to a physical therapist with back pain and a midsection that is any less impressive than an Olympic gymnast, it is a mortal certainty you will be told to strengthen your core. What is the evidence that poor core strength causes pain or that core strength exercises reduce back pain?
Before reviewing the studies, it is first interesting to note that most of life requires only minimal activation of the core musculature. During walking, the rectus abdominis has an average activity of two percent of maximal voluntary contraction, and the external oblique operates at five percent. During standing, trunk flexors and extensors are estimated to fire at less than one percent. Add more than fifty pounds to the torso and they fire at three percent. During bending and lifting muscular activation is similarly low. Given that daily life seems to require so little core strength, perhaps it is not surprising that research interventions to increase core strength have little effect on pain.
For example, one study showed that core strengthening exercises for pain free persons identified as having a weak core do not reduce the future likelihood of back pain. Numerous studies have been performed to test whether core strength exercises reduce back pain. The thrust of these studies is clear – although these exercises can improve low back outcomes, it works no better than general exercise. The obvious conclusion is that if core strengthening has any benefit at all, it works only because of the generally beneficial effects of exercise (or as a placebo), not because the core is a special area of concern. In other words, despite what we are told over and over, the current evidence states that there is nothing magic about core strength as means to prevent or reduce back pain.
The above results are surprising and counterintuitive, and raise many questions such as: why do these approaches seem to work; how can so many people be wrong; and if these aren’t the true sources of pain, then what is? I will try to answer some of these questions in the next post. For now, I will say that all of the above approaches all share a fatal flaw – they look for the source of pain in the mesoderm, the structure of the body, when pain is in fact in the exclusive control of the ectoderm, the nervous system. I’ll look at that issue a little more in my next post.
*Most of the studies referenced in this article are from three excellent papers: The Myth of Core Stability by Eyal Lederman; The Fall of the Postural Structural Model in Manual and Physical Therapies by Eyal Lederman; and The Traditional Mechanistic Paradigm in the Teaching and Practice of Manual Therapy: Time for a Reality Check, by Frederic Wellens.